This invention relates to electromagnetic projectile launching systems and more particularly to launch packages for such systems which include a conductive armature for initial acceleration and a plasma armature for additional acceleration.
Electromagnetic projectile launchers are known which comprise a pair of conductive rails, a sliding conductive armature between the rails, a source of high current and a switch for commutating this current into the rails and through the armature. Current flow through the rails and armature results in an electromagnetic force on the armature which propels it along the conductive rails. Launchers which utilize a sliding metallic armature have experienced considerable rail damage caused by failure of the sliding armature in the breech region. Metallic armatures are also limited by resistive heating and their ability to respond to rail unevenness at high velocities. In these cases, a plasma or arc armature may be more suitable.
The principal disadvantage to the use of a plasma propelling armature has been the damage that occurs to the breech section of the launcher rails during formation of the plasma. Once the plasma is moving at substantially high speed, very little, if any, rail damage occurs. U.S. Pat. No. 4,347,463, issued Aug. 31, 1982 to Kemeny and Litz, discloses a means for establishing an arc for propelling a projectile comprising a shooting wire or fuse which initiates current flow between the rails, disintegrates, and thereby forms a plasma or arc through which current continues to flow. After the fuse explodes, the plasma exerts a force on the projectile and accelerates it to a high velocity, while debris from the fuse explosion is left behind in the barrel breech section. Because the mass ratio between a projectile and a plasma armature is greater than that between a projectile and a sliding metallic armature, more efficient utilization of a given available launch package energy is possible with plasma drive. In addition, plasma drive provides a means for launching ultra high velocity projectiles. Therefore the application of plasma driven projectiles in multi-shot systems is appropriate.
Several methods have been suggested for initiating an arc or plasma in electromagnetic launcher systems. These procedures are primarily directed to resolving the problem of creating the plasma armature and minimizing the resulting thermal and mechanical damage of the launcher rails. Ablation of the rail surfaces is caused by a slow moving or stationary arc and occurs during initial acceleration of the projectile from zero velocity. At higher projectile velocities, the effect of this thermal phenomenon becomes increasingly insignificant. Therefore a means for imparting initial momentum to the launch package is desired to prolong launcher rail life. Copending commonly assigned application entitled "Electromagnetic Projectile Launcher With Explosive Start and Plasma Drive", Ser. No. 399,509, filed July 19, 1982 by Ross, discloses an electromagnetic launcher which utilizes an exploding fuse in an air tight insulating cartridge to generate a plasma with sufficient pressure to impart starting momentum to a projectile thereby increasing initial arc velocity.
Excessive launcher rail damage has been observed where a copper fuse is blown to form a plasma composed mainly of copper ions. This resulted in sputtered metal from a partially vaporized fuse and thermal erosion of the rail surfaces from a slow moving or stationary arc over only a short length of rail starting at the original location of the fuse in the breech. Therefore the design of a fuse and an interface between the fuse and a projectile must consider the usual design criteria of desired fuse explosion time and peak voltage after fuse explosion, as well as other factors which include: reducing the explosive damage to the launcher barrel and projectile; minimizing the time that the fuse mass must be accelerated; and handling the fuse debris so that dielectric problems are eliminated. A launch package constructed in accordance with the present invention addresses these factors and provides for the additional benefit of reduced barrel rail damage during the initial stage of plasma acceleration.